Tracer control circuit for machine tools



June 14, 1960 s. cuDNoHUl-'SKY TRACER coNTRoL CIRCUIT Foa MACHINE Toons 5 Sheets-Sheet 1 Filed Aug. 29, 1958 June 14, 1960 s. cuDNoHUFsKY TRACER CONTROL CIRCUIT-FOR MACHINE TOOLS 5 Sheets-Sheet 2 Filed Aug. 29, 1958 WGILHRII w .s w Rf f mw m o e V w o N a 7 I W wld .k Y HB |114 1 .a 0\\ n W/Twn n !IH Pw fili.Ill.J OQ NV n I l. will?? l i I IIL rl' I l l I N l L l SRV@ .WC ww 3v vw uk.. ow om, UN mvN June 14, 1960 s. cUBNoHuFsK-Y TRACER CONTROL CIRCUIT FCRMACHINE TooLs 5 Sheets-Sheet 3 Filed Aug. 29, 1958 y s K v, mm. w a .n T m 0 m M WM C mw@ [Y :I .WB s

June 14, 1960 s. cuDNoHUFsKY TRACER CONTROL CIRCUIT FOR MACHINE TOOLS 5 Sheets-Sheet 4 Filed Aug. 29, 1958 INVENTOR.

A Trae/v' ya `Fume E4, 1960 s. cuDNoHUFsKY IRACER CONTROL CIRCUIT FOR MACHINE TooLs 5 Sheets-Sheet 5 Filed Aug. 29, 195e llllH VAE 2 e INVENTOR.

6HL/5751? Cao/va//z/FJA'Y United States Patent 2,940,263 TRACER CONTROL CIRCUIT FoR MACHINE rooLs Sylvester Cudnohufsky, 3650 Lapeer Road, Pontiac, Mich.

Filed Aug. 29, 1958, Ser. No. 758,126

34 Claims. (Cl. 60--97) This invention relates to improvements in tracer control circuits for governing the automatic operation of pattern-controlled machine tools.

Pattern-controlled machine tools are usually provided with means for moving the cutting tool in two perpendicularly related directions by means of a pair of hydraulically controlled piston-cylinder assemblies. The degree of relative actuation of the two piston-cylinder assemblies so as to produce movement of the cutting tool angularly is often determined by the movement of a single stylus or nger in following a template or pattern which in turn controls a tracer valve. The design of tracer control circuits capable of causing a stylus to accurately follow an irregular contour on a template or pattern has usually involved the use of a very complicated valve arrangement which includes numerous valves that have been considered necessary to insure an accurate tracing movement of the stylus relative to the template. Even with such complicated valve arrangements, difficulty is very often encountered where the angular change in direction on the pattern is relatively great.

Another problem that has presented itself in connnection with tracer control circuits is the necessity to reduce the feed rate as the stylus undergoes a change in direction of movement to avoid cutting on the workpiece a transition line resulting from the momentary opening or closing of a valve in the control circuit.

It is an object of the present invention to provide a tracer control circuit for machine tools which is of relatively sirnple design and which, at the same time, is capable of producing an extremely accurate following of the pattern or template by the tracer stylus or finger.

A further object of the invention resides in the provision of a tracer control circuit involving a single tracer valve in combination with a minimum of other valves.

Another object of the invention resides in the provision of a tracer control circuit which includes a relatively simple valve arrangement that enables feeding of a cutting tool in either of two opposite directions in a pattern controlled manner.

A further object of the invention is to provide a tracer control circuit designed such as to eliminate the necessity for reducing the feed rate as the stylus undergoes a change in direction.

A still further object of the invention is to provide a tracer control circuit wherein the valves controlling the operation of the feed cylinders during the tracing cycle are in the nature of ow control valves as distinguished from directional valves so that feed cylinders are controlled by the rate'of ow and not by the opening or closing of valves.

Other objects and advantages of the invention will become apparent from the accompanying description taken with the drawings, in which:

Fig. 1 is a diagrammatic view of a tracer control circuit embodying the present invention, the various valves 2,940,263 'Patented June 14, 1960 2 being sho'wn in the positions assumed when the circuit is energized and running idly.

Fig. 2 is a view similar to Fig. l showing the control circuit conditioned to cause the tracer finger to approach the template. Y

Fig. 3 is a view similar to Fig. 1 showing the control circuit conditioned for initiating the tracing cycle, that is, for causing the tracer ringer to follow the pattern of the template.

Fig. 4 is a view similar to Fig. l showing the control circuit conditioned to retract the tracer finger to the starting position.

Fig. 5 is a semi-diagrammatic sectional view of the tracer valve.

In the drawings, the tracer valve is generally designated 10 and has a finger or stylus 12 mounted thereon for tracing the contour of a pattern or template 14. To illustrate the operation of the improved control circuit of this invention, it may be assumed that the tracer is used on a lathe. On such a machine tool, the template 14 could be fixedly mounted on the bed of the lathe and the tracer valve 10 could be mounted on the cross slide of the lathe which is generally designated 16. A cylinder 18 mounted on the carriage 20 of the lathe houses a piston 22 which is connected by a rod 24 with cross slide 16. A cylinder 26 encloses a piston 28 which is connnected by a rod 30 with carriage 20. Actuation of piston 28 causes the stylus 12 to be fed in a longitudinal direction while actuation of-piston 22 produces movement of stylus 12 in a transverse or cross feed direction normal to the longitudinal feed. The cutting tool, generally designated 32, is shown mounted on the cross slide 16. The source of hydraulic fluid under pressure for operating the two cylinders comprises two pumps 34 and 36. Pump 34 may be referred to as the low pressure pump capable of developing a relatively low, substantially constant pressure, say 400 pounds per square inch. Pump 36, on the other hand, is referred to as the high pressure pump which is capable of instantaneously developing a relatively high pressure, for example, 1,000

pounds per square inch.

The means for controlling the directional ow of hydraulic iluid through the circuit comprise two pilot controlled valves 38 and 40. Valve 38 is a four-way solenoid controlled, pilot operated, valve of the springcentered type. Valve 4i) is a two-way valve of the solenoid controlled, pilot operated, spring-offset type. The pilot valve component of valve 38 is designated 42 while the main directional valve component of valve 38 is designated I445.. Likewise, in the case of valve 40, the pilot component is designated 46 and the directional valve component is designated 48.

Low-pressure pump 34 connnects with the directional valve 44 by means of a line 50. Within this line, there is arranged a sequence valve 52 of the external drain type. The head end of cylinder 26 is connected with the directional valve 44 by a line 54 while the rod end of cylinder 26 is connnected with the directional valve 44 by a line 56. Pilot valve 42 is connected to pump 34 through a line 58. Pilot valve 42 is of the conventional type including two solenoids 6i) and 62 for shifting the spool of the valve in opposite directions. The opposed operating cylinders 64 and 66 are connnected with the pilot valve 42 by means of lines 68 and 70, respectively.

For the purpose'of simplication, in the drawings the pilot oil lines are shown as broken lines while the actual ilow lines of the control circuit are shown in solid lines. Furthermore, the oil lines which are operative in the particular portions of the cycle illustrated in Figs. 1, 2, 3 and 4 are shown in heavy lines and the oil lines which may be considered as idle are shown in light lines.

The inlet port of tracer valve 10 is connected with traced without any difficulty at all.

'spool of valve 46 is shifted to the right 'under the iniiuence of spring 160 and, as illustrated, the pilot line 80 is thus connected to actuate cylinder 84 and thus shift the spool of directional rvalfve 48 to the rightrand thereby stop the flow of oil to the sump through line 78. 4Upon the closing of directional valver48, the pressure of the oil flowing from pump 34 through line 50 builds up to a value such that the force on the underside of piston 22 exceeds the force on the upper side of pistonn22 (orice 154 in the tracer valve is Ywide open)y and the cross Slide 16 is fed inwardly toward the work until the stylus 12 contacts the at surface portion 162 at one end of template 14. When the stylus 12 contacts the surface 162, oriiice 154 in the tracer valve is immedi; :ately restricted and the pressure of the oil in 'lines 72 .and 75 immediately builds up to a Value wherein the forces acting upon the opposite sides of piston 22 balance 'one another and the cross slide 16 thus remains stationary with the stylus 12 contacting the surface 162 -of template 14 with the predetermined force for which the tracer valve is designed, as described previously.

With the stylus 12 thus properly advanced into contact with one end of the contoured surface of the template 14, the feed portion of the tracing cycle may be initiated Tby energizing either of solenoids 60 or 62 of pilot valve 42 (Fig. 3). In the arrangement illustrated, the tool is being shown fed from left to right; and thus, in Fig. 3, the solenoid 60 is shown energized. When solenoid 60 is energized, the oil in the branch pilot line 58 is conducted through pilot valve 42 to the cylinder 64 of directional Ivalve 44. Thus, the oil`V in line 50 from the low-pressure pump 34 is directed through the directional valve 44 and through the line 54 to the head end of cylinder 26. The carriage 2t) is thus fed in adirection to the right and the rate of feed is controlled by the rate at which the oil is displaced from the rod end of cylinder 26.

As piston 28 in cylinder 26 moves to the right, oil is discharged from the rod end 'of the cylinder through line 56 and through the directional valve 44 to the line 92. The pressure of the oil in line 92 balances the pressure of the oil in the head end of cylinder 1S so that piston 22 remains stationary in cylinder 18 and all the oil displaced from the rod end of cylinder 26 is discharged from the system through the ow controlV valve 192, As mentioned previously, valve 102 is of the pressure compensated type so that regardless of the pressure in the lines, the ow through valve 102 never exceeds the maximum value for which it is set and the maximum rate of longitudinal feed of the carriage is thus controlled.

When the stylus 12 moves on to the forwardly inclined surface 164 on the template, the contact pressure of the stylus against the template is momentarily relieved. The stylus tends to pivot clockwise about the adjusting screw 148 at the left, thus instantaneously reducing the restriction at orifice 154 in the tracer valve and causing the back pressure in line 72 and in the rod end of cylinder 18 to drop slightly. In response to the drop in pressure in the rod end of cylinder 18, the cross slide 16 feeds inwardly while the carriage 20 is moving to the right and the stylus is thus caused to follow the forwardly inclined surface 164 on the template.

It will be appreciated, of course, that ifrthe inclination of the forward incline shown at 164 on the template is too steep, then the maximum opening of orice 154 as determined by adjusting screws 148 will be incapable of bypassing oil at a sufficiently rapid rate from the rod end of cylinder 18 to maintain the stylus in contact with the template at the longitudinal feed rate for which the tracer is set. However, experience has shown that with the tracer control circuit described herein, a forward incline as great as 3 to the longitudinal can be Forwardly inclined shoulders of even greater than'30 have been success- 6 fully traced with this control circuit. The setting of screws 148 determines the rate of transverse feed inwardly. However if screws 148 are backed off too far, then the stylus 12 has a tendency to pivot about the screw 148 at the left too freely when the stylus encounters a forward incline and the cutting tool will have a tendency to plunge into the work.

yAs the stylus follows the forwardly inclined-surface 16,4 konthe template `and encounters the straight longitudinally extending surface 166,` there is a momentary and instantaneous greater `restriction at the orifice 154 in the tracer valve;V and there is a corresponding instantaneous and momentary increase in back pressure` in lines .72 and 75 and the rod end of cylinder 18. The forward feed of the cross slide 16 is thus arrested, since, as previously described, the pressure of the oil in the rod end of cylinder 18 automatically and instantaneously establishes itself at a value producing an equilibrium condition of the piston 22 in cylinder 18.

Eventually, the stylus 12 encountersthe reversely inclined surface 168 on the template. When this occurs, the stylus tends to pivot counterclockwise about the adjusting screw 148 at the right, thus effecting an in.l stantaneous and momentary greater restriction of the oriiice 154` in the tracer valve to an extent such that the back pressure in lines 72, 75 and the rod end of cylinder 18 increases to a value where the force acting on the top side of piston 22 exceeds the force of the oil acting on the bottom side of piston 22 and the cross slide is progressively retracted as the carriage continues to move in the direction toward the right. When this occurs, it will be appreciated that oil is discharged from the head end of cylinder 18. Since oil flows through the line 76 and since the directional valve 48 is closed to the sump, the oil discharged from the head end of cylinder 18 is caused to ow through the ow control valve 96. The check valve in ow control valve 96 restricts the flow of oil through the valve to the metering orifice 170.

In this connection, I have discovered that the arrangement of ow control valve 96 asshown is necessary to prevent va surge of oil in the head end of cylinder 18 and the consequent lopping or chattering of the stylus as it travels along the reverse incline 168. Without the provision of a flow control valve such as illustrated at 96, I have determined that the provision ofthe flow control valve 102 alone for. controlling the rate of discharge of oil from the head end of cylinder`18 is incapable of preventing the stylus from surging back as it travels along the inclined surface 168 ofthe template. Flow control valve 96 lserves as a dampener between the head end of cylinder 18 and the flowpcontrol valve 102. In practice, flow control valve 102 is set to produce the desired rate of feed of the carriage. Under normal flow conditions, the settingof valve 96 is such as to restrict the ow to a greater extent than the flow is restricted through valve 102. The proper setting of valve 96 is,v however, very easily obtained. When the stylus 12 encounters a reversely inclined surface such as illustrated at 168, the orice of valve 96 is simply progressively closed until a point is reached where the stylus no longer surges back from the inclined surface. Since valve 96 is not of the pressure compensated type, the volume of flow through the valve is responsive to the pressure of the oil in the head end of cylinder 18. However, the rate of discharge of oil from the system, and therefore, the rate of feed of the stylus, is at all events controlled by the valve 102 and thus maintained at a uniformly constant value. Y

Thus when the stylus encounters a reversely inclined surface such as illustrated at 168, a portion of'the oil flowing to sump 103 through flow control valve- 102 is that which is displaced from the rod end of cylinder, 26 and another portion is that which is displacedyfromJthehead end of cylinder 18. The maximum ow,which t 7 Y Y determines the kfeedrate, is at all events controlled thesetting 'ofva`lve'102f 'When'frhe sjaals-,12 :e counters the 'straight shoulder Y 172 oir-the" mpl'a't'e, 4"there is again lan immediate land mornentaryeicreas'e vthe restriction: 'at orifice Y-154 in the'tracervali/"e, Consequently; thef1back-pressure in' lines 72,- 75 and the rod end of cylinder liinmieliately Y is retracted. 'Ijhe `'press'tir'e-offtherJilin'llines '7.6 and l.93VV Y immediately 'builds iup to a value greater than the-majri-r Y mumpres'surethat is capableoffljengldeveloped gitt line 92 by pump'. `ilhu's, the longitudinal `feed vof the 'carriage ',201` 'is instantaneously 'arrested; and theoil Adischarged from j'th'eV system' through the flow control #valve 1Q2 is [thato'il which A:isheing displaced byf'the inward or 'downward movement -of Vpiston 22 in cylinder (13.V

couldl be anchored rson* the carria'ge and -the'cylinder :18' connected to the cross slide.l Likewise, the Ypiston rodv 30 could he.V xed atl oneen'd on the hed 'of -the machine and ythe cylinder-26 connected to the carriage. `It

also fbe appreciated that 'the specitlcV pressures hereto- Y Afore recited'have been rstatedmerelyforftlleV purpose "off illustration,andI-no'tbywvay. of limitation. Y11t isV the :relative i pressuresv {capahle Yof. beingVV developed irr the lines 50 and f` '-Zi that are,important. Itis essential that the pump "l 3`6'bje apahle vof"generatlingfa substantiallyhigher pres- 'pump 34 so-that at 4'al,l'events, thel forceacting Y o'n'ther op side V'ofltiston 22 is *capable ofvexceeding the 'force 'developed Von thebottomsideof the pistonV 22 so thatthe'carriage'can'be retracted.Y

Thus it'lwill be s'een'ft-hatV the'ltraeer control circuit` Y of this invention utilizes 'a single ltracer valve for controlling'the operationfof fbothfeed Cylinders iand a -minimum o'o'ther valves The valves operative Yduring the tracirfg'cyc-l'e 'are rallfin the nature ofilow rate controlling valves. 'eThejoil ilo'wthrough vthe circuit never stops in order 'toetect-'a change ,in speed'or direction. Thus the operationlissmooth'andfcontinuous at all times. This in'turnfeuables thelutilization of la highfrate `of feed without'atendency forthe cutting A'tool to leave a transition lihefon Ythef-Worlgpiec'e 'When-the stylus encounters Y af different incline'fro'm' that on which it has been traction r'eversely to' the longitudinal "feed," then 'fit is iclear that thecarriage 20 must'be capabl'ejofb'eingjreti'acted by thepist'on `Zjiu cylinder 26. .V`Valvef94 is fset suchthatl its `oriice174 is ionly"slightlyopen. Thus, -if template 14 should becomecockedasidescrib'ed,theback'pressure inline 72 and in the'rodiend of cylinder '1'8"W`illfimmedii ately'rise 'to a sufficiently highA v'alue'to'cause aportion of 'the oil discharged 'from'V the headfendof cylinder 18 to feedback Vthrough valve 94 AandA into'the 'rodi end o cylinder'26 toren-act thepiston 28E-therein.'

Relief valvefitlris Valways-set to 'relieve p'ressureat a higher value than jthe setting ofrelief valve 1t4so that the pressurein'the rod-end of cylinder 18 `.can at all v times exceed the pressurein -the'headendot this cylinder.

It is this relative 'setting' otrelief valves andf 1% Y ing.-Y ;This YisV extremely important in' machining Work pieces that require a high .degree Cif/accuracy. `With the tracer control circuit of 'thiseinvention the Vrate of Yfeed is fnot determined: by any limitations Ainherent in theoperation Vof the circuit but rather bythe particular vma- Y chining'operationbein-g performed.

This application is a continuation-'Vin-partgof my 'co pending application Serial No. 476,426, lfiled December 20, 1954, novv abandoned.

l. In a tracer control circuit for governing Vthe operation'of afpairof'fe'ed cylinders arranged to yfeed acutting Atool vin angularly related directions, Ythe combination of two sources of hydraulic pressure', one being'capable ofy developing a'higher pressure than the other, va

that'enables thelo'ng'itudinal feed'to be' arrestedwlrenever "necessary Y Y Y I n Y Relief valve 108 alsovserves, as a safety valve'inl the Y `Vcircuit.` liftl'le'oil"lines'betvveen the/:head endof'cfylinderY *i 18 and *ilowfuc'ontrol valve 102 Yshould'becomev clogged for any reasonjandthe stylus 12 `'shouldl'encounter a" ,shoulderthat requires retraction ofthe cross slide, then Y. l

Vtheexcessive backgpressure-that would'gbebuilt upin Y line 7.2'would'be" bledback into'the rod 'endj'ofr cylinderv Zothrough reliefV valve'1'08 and'line92. For this reason,"Y

, yalve 10S isset to'relievet-the pressureinfline '72 ata n value-intermediate the settings ,of1va'lves'1t4'and 106.V When'the'pressure in line V472jtends -to exceed thesettirrg'V Y offvalve'flt, valve tlsimply opensandthe longitudinal Y lfeed-ofthefstylusris immediately arrested.

AvAf-ter'the stylus has completedY itsftravel'along the contoured VsuriraceofY the'template and it isV desired to Vreturn lthe Ystylus tothefstarting position illustrated in Fig.VA l, aswitchfnot illustrated,V is actuated to Yenergize solenoid 158 Iof the lpilotfvalve -46 ^and-solenoid 62` of pilot'v'alvef42. Simultaneously therewith, -solenoidjil tracer Valve, Va feed lineconnecting thetracer valve with the source ofV higherV pressure, pattern controlled actuating means 'for controlling* the tracer valvei toV variably i restrict Athefilow therethrough and'thereby Vvaryrthefpressure in said jieed line, means 'connecting'theieed line Vwithjoneendof Yone of saidVV cylinders, a 'feed line extveuding'from saidsource @flower pressure to oneer'id ofltheother cylinder, a 'common discharge( line-connecting therotla'erk ends of said cylinders;to exhaust, means in Vsaid discharge line Vfor(permittingfree ow therein in a direction fromVV the YsecondV cylinder to `the first, and for prevcntiru7 freeliow in the oppositerdi'rection' and-'means l'in ysaidV discharge line for restricting;l the rate offlow from said line to exhaust to a predetermined fmaximum value.

12. The combination set forth in claim l Vwhereinrsaid last mentionedmeans comprises a pressure compensated ow control valve. Y

3. The'combination set forth in `claim lliirtcluding means in said discharge line locatedbetvvecn said-'last in the 'position assumedr forV retraction 'of the stylus.V Withthe- 'valves 'in the positions illustrated, the head end offfcylinder -26-andthe head end' of cylinder v18 Yare both 'connected' to thes'ump'through thejdirection'al valve 48 espective `'cylindt'e'rs vtandtheistylus isa Y mentioned means and said rstcylinder for limiting. the

rate of owffrom the'iirst cylinder Ytosaidlast mentioned means'to a valuenormally lessthanthe maximum rate of flow ,permitted Vby said last mentioned means'to eX- haust. n Y t, t Y n Y V4. in a tracerv controlcircuit for. governing-therapeutiorroi a pair of hydraulicV feedingdevi'ces oa patterncontrolled machine, theA combinationoiafsourceof rela- 1 tivelyhigh pressure, Y.means connecting oneof saidfeeding devices withI said V:sourced l,of highpressure, atracer valvejforjcontrollingrthe vpressure of they fluid/'supplied Vby said.'- source; to fsaid onei :feeding device; a soureeof lower pressure,means-connecting thefsonree :offlowenepressure fle-10,2%

v to the other feeding device, a return line extending be tween said feeding devices, means in said `return line permitting free flow therethrough in the direction from said other feeding device to said one feeding device and preventing free flow therethrough in the opposite direction and means restricting ow from said return line to ex# haust at a predetermined maximum rate.

5. The combination set forth in claim 4 including means for optionally connecting said return line for free iiow to exhaust.

6. The combination set forth in claim 4 wherein said last mentioned means comprises a ow control valve arranged to limit the flow to exhaust to a maximum rate independently of the pressure in said return line.

7. The combination set forth in claim 6 including a second ow control valve in said return line between said tirst mentioned tlow control valve and said one feeding device, said second tiow control valve being arranged to limit the maximum ow from said one feeding device towards said first valve at a maximum rate which varies with the pressure.

8. The combination set forth in claim 7 wherein said second ow control Valve normally restricts the iiow to a rate less than the maximum rate permitted by the first flow control valve.

9. In a tracer control circuit for governing the operation of longitudinal and transverse feed cylinders of a pattern-controlled machine tool, the combination of a source of pressure, a second source of pressure capable of delivering a pressure higher than said first source, a feed line extending from said source of higher pressure to one end of said transverse feed cylinder, a tracer valve for regulating the pressure in said feed line, a feed line connecting the source of lower pressure with oneend of said longitudinal feed'cylinder, a return line extending between the other ends of the two cylinders, means in said return line permitting substantially -free flow in the direction from the longitudinal feed cylinder to the transverse feed cylinder and preventing free flow in the opposite direction and means for permitting flow from said return line to exhaust at a restricted rate.

10. The combination set forth in claim 9 wherein said source of higher pressure is connected with said transverse feed cylinder such that an increase in pressure in said first mentioned feed linetends to produce'retraction in said transverse feed cylinder.

11. The combination set forth in claim 9 including means for optionally connecting said second feed line to either, end ofsaid longitudinal feed cylinder.

12. 1The combination set forth in claim 9 Vincluding means foroptionally connecting said second feed line directly with said return line and said return line directly with exhaust.

13. The combination set forth in claim 9 including means responsive to an increase in pressure in said first mentioned feed line above a predetermined value for con-. necting said first mentioned feed line with said return line at a point upstream from said means for preventing free tiow in said return line.

14. In a tracer control circuit for governing the operation of longitudinal and transverse feed cylinders of a pattern-controlled machine tool, the combination of a source of pressure, a second source of pressure capable of delivering a pressure higher than said rst source, a feed line extending from said source of higher pressure to one end of said transverse feed cylinder, a tracer valve for regulating the pressure in said feed line, a feed line connecting the source of lower pressure with one end of said longitudinal feed cylinder, a return line extending between the other ends of the two cylinders, spaced apart first and second means in said return line for permitting substantially free liow therein in the direction from the longitudinal feed cylinder to the transverse feed cylinder and preventing free ow in the opposite direction, a discharge line to exhaust connected to said return-line intermediate said last two mentioned means and a ow` ontriV valve in said discharge linek for restricting the rate of ow to exhaust to a predetermined maximum value .independ ently of the pressure in said return line.

l5. In a tracer control circuit for governing the opera-l tion of longitudinal and transverse feed cylinders of a pattern-controlled machine tool, the combination of Ia source of pressure, a second source of pressure capable of delivering a pressure higher than said first source, a. feed line extending from said source of higher pressurey to one end of said transverse feed cylinder, a tracer valveY for regulating the pressure in said feed line, a feed line connecting the source of lower pressure with one end of said longitudinal feed cylinder, a return line extending between the other ends ofthe two cylinders, means in said return line permitting unidirectional free ow therein from said longitudinal feed cylinder to said transverse feed cylinder, a discharge line connected with said return line and having means therein for restricting the maximum rate of ow from said return line to exhaust to a predetermined amount, said discharge line being connected with said return line on the upstream side of said unidirectional ow control means.

16. The combination set forth in claim 15 including means in shunt relation with said unidirectional ow control means for restricting the rate of liow from said transverse feed cylinder towards said discharge line in response toy the pressure in said return line between said 'transversey feed cylinder and said unidirectional ow control means.,

17. The combination set forth in claim 16 wherein said second mentioned iiow control means normally restrict the flow to an extent greater than said firstY mentioned flow control means.

18. In a tracer control circuit for governing the opera tion of longitudinal and transverse feed cylinders of a pattern-controlled machine tool, the combination of' a source of pressure, a second source of pressure capable of delivering a pressure higher than said first source,` a feed line extending from said source of higher pressure to one end of said transverse feed cylinder, a tracer valve for regulating the pressure in said feed line, a feed line connecting the source of lower pressure with one end of said longitudinal feed cylinder, a return line extendingbetween the other ends of the two cylinders, means lin said return line permitting free ow therein in the direction from the longitudinal feed cylinder to the transverse feed cylinder and permitting metered iiow therein in the opposite direction, an exhaust line connected with saidv return line between said last mentioned means and said longitudinal feed cylinder, and means in said exhaustV line for controlling the maximum rate of flow therethrough to an amount normally less than the rate of ow permitted by said flow metering means in said return line.

19. The combination set forth in claim 18 whereirrsaid ow metering means controls the iiow in said return line in response to the pressure therein and wherein the ow control means in saidv exhaust line restrict the flow therein to a maximum rate independently of the pressure in said exhaust line.

20. The combination set forth in claim `19 including a second means in said return line located between said longitudinal feed cylinder and said exhaust line for permitting free flow in said return line from said longitudinal feed cylinder towards said transverse feed cylinder and for permitting metered flow in the opposite direction.

21. The combination set forth in claim 20 wherein said last mentioned ow metering means are arranged to restrict the iiow in said return line to said longitudinal feed cylinder to a maximum rate substantially less than said tool, the combination of a source of relatively high-pressure connected to one end of the feed cylinder, azsource` of"relativelyr=low, substantiallyfconstant pressure/Ycon- Y nectedtothe opposite -end of the -feed cylinder, a tracer valveiconne'cted with said source'of relatively high pressure for controlling the pressure in said cylinder at said one end thereof,rmeans permitting unidirectional Yfree Y Yiiow from lsaids'ource 'of low r'pressure to saidropposite endiof saidrcylinder, and means for discharging oil' from said oppositeend of -saidfcyrlinder to exhaustata controlled rate.'

'23. Y In -a :tracer controlcircuit for governing theropera-` tioned feed line limiting Vthe free riiow therein to a direc-V tion from said low pressure source of pressure to said feed cylinder, ani exhaust line `connectedfwith said otherV end of said cylinder on the downstreamside of said'last rnentioned means and means Vin said exhaust line for restrictingi-the rateof-exhaust flow therethrough'toapredetermined maximum value. Y

24. The combination `Vset forthr in claim 23 including pattern controlled means for Aactuating `said tracer valve,

Vsaid .tracer valve having an adjustable orifice therein com- Vmunicaringwith said -iirst mentioned feed line', said pat- Y terncontrolled Vactuating means being responsive to vary the .size of saidvorice to control the pressure in said feed line Yand thereby control the direction and rate of operal' tion ofsaid feed cylinder. Y

i: 25. The combination set forth in claimr4 .including pat- Y ternV controlled actuating means for said tracer valve, said tracer valve having anadjustable orifice therein communicatingwith said means connecting'oneof said feeding deviceswith said source of high pressure, said actuating means being adapted to vary the size of lsaid orifice `to controlthe pressure in said last mentioned connecting' means .and thereby control the rate and directionof relative movement of said two feeding devices. Y A

26. Ina tracer control circuit for governingV the operation .of a feed cylinder of a pattern controlled machine tool, Ythe combination ofa source ofrrelatively low,fsub-'y stantially constant pressure, a feed line .connecting said low pressure source with one end of said feedcylinder, a sourceof relatively high pressure, Va feed line connecting said .high pressure'source Vwith the. opposite end of .said feedcylinder,` a tracer control valve having ,an Vinlet vport communicating with said last mentioned 'feed' line, said tracer valve alsohaving anY outlet port and a Vrestrictable orifice between said inlet and outlet ports, means ,connectingsaid outlet port with exhaust, pattern controlled Vactuating means for controlling the degree of restriction of said orilice, .said orifice when fullyropen being, adapted to accommodate the fluid flow from saidvhigh pressure source without appreciably increasing the pressure there- Y of, whereby under said conditions, the feed cylinderlis actuated in one direction under the bias of said relatively low, -generally constant pressure, and when said pattern controlled actuating means produces restriction at said orifice, theV ba'ckpressure in said high pressure feed lineV f opposes therelatively low, substantially constant pressure at said oneV end lof thel feed cylinder to control. the rate 3 and direction of. operation of said feed cylinder.

' 27. In atracer control circuit Yfor governing theoperation of a feed cylinder of a pattern controlled machine tool, the combination of a source ofrelatively low, substantially constant pressure, a feed line connecting'saidk low pressure source with one end of the 'feed cylinder, source of relatively high Vpressure, `a feed line connecting saidfhigh pressure sourceV with the other end ofthe Yfeed cylinder, 'atracerY valve Yhaving an inlet V`port 'and anfoutlet nsy port, apassageway in said valveconnecting'said-inlet and outletfportsfa restrictable orifice-in said passageway,` said inlet portcommunicating withsaid relatively high pres-l sure-source, said outlet Aport being connectedl-toexhaust and patterncontrolled .actuating means for said tracer Valve, said .pattern f controlled --actuating means :being adapted to varyvtherestriction ofpsaid orifice, said orifice when Vfully open being capable ofaccomrno'dating the ilow from said relatively high pressure source withoutappre-t ciably increasing the pressure thereof wherebyunderfsaidcondition, the feed'cylinderis' actuated in one direction under the bias of said `generally --constant Ylow pressure, and when said pattern Icontrolled wactuating'means produces restriction Vat said orifice, the back pressure thereby produced at said otherendof the feed cylinder opposes the low pressure at saidonelend ,of the feed cylinder toV control the frate andidirection of voperation'of sai'd vfeed cylinder.

28. The combinationset forth in Aclaim 27 including connecting said Slow pressure source withthechamberonV one side'of the Ipiston,-a source of relativelyiiigh pres-- sure,'a 'feed lineV connecting said YIl'righ pressure sourcev with the chamber on 'the opposite'side-o'f the piston, `a tracer valve having an inlet'andN an outlet,V a'passa-geway connecting said inlet and said outlet and-|l1avingga 'restrictable .orifice therein, saidinlet communicatingwith said source'of relatively high -pressure and said outlet communicating with exhaust, pattern controlled actuating means for varying the degree of restriction of said orifice, saidforitice when fully open being capable of accommodating the uid flow from said source of `relatively high pressure withoutY appreciablyfincreasing thepressure thereof, whereby under said condition,'the piston will moveV in one direction under the -bias Vof said-generally-constant pressure and when said yactuating means produces restriction at said orifice,Y thebackpressure resulting therefrom Yis effective inl the chamber' at said' other side o f the piston to'oppose the `generally/constantY pressure in theohamber on' the'rst mentioned sideof the piston whereby the piston moves relative to the cylinder in a -direction and at a lratel responsive'to the.; degree of restriction* at said orifice lproduced byV said' Vpaftter'n controlled actuating means. s ,Y

30. The combination set forth in Yclaim .29,l including means VIfor limiting the rate of exhaustfrom the Vchaniber connected with ksaid Ysource i of Yrelatively lowlconstant pressure. Y l f 3l. In a tracer valve'V-for'a pattern controlled Vmachine tool, the combination of a valve body lhaving a bore therein, said bore having at yleast two axially spaced portions of ydifferent diameters, a spool within Vsaid' .bore

having a first portion slidably engaging within the smaller v diameter portion of the :bore and a second larger diameter portion cooperating with the largerV bore portiontoformY an orifice, the size of which varies progressively in ac- Y' cordance with the axial movement of the spool in the bore, 'an inlet on said :body communicating with the :larger bore portion on the side of the orifice adjacent the smaller diameter portion of the spool, an exhaust port side of the orifice, whereby when pressure fluid is admitted toV said valvethrough said inlet portjthe spool is` {biase'd axially in a direction'tendingto i-ncreasethe siaefofsaid oriiicejand ya-stylus movablylmounted on said valve `bodyandzoperably connected wthsaid spooi.

' slidably engaged within the smaller bore portion, the

larger piston providing a shoulder cooperating with a portion of the larger diameter bore portion to form an orifice in said bore, the size of which varies progressively with the axial movement ofthe spool, an inlet port on the body communicating with the larger bore portion on the side of the orifice adjacent the smaller piston, an exhaust passageway in said valve communicating with the portion of the bore on the opposite side of the orice, whereby when pressure uid is admitted to said valve through said inlet port, the spool is biased axially in a direction tending to increase the size of said orifice and a stylus movably mounted on said valve body and operably connected with said spool.

33. A tracer valve as set forth in claim 32 wherein said stylus is mounted on the valve -body for pivotal movement and including an axially shiftable member interconnecting said spool and stylus.

34. In a tracer valve tor a pattern controlled machine tool, the combination of a valve lbody having a bore therein, said bore having at least three axially spaced portions of progressively increasing diameters, an axially movable spool in said Ibore, said spool having one portion slidably engaging the smallest bore portion, said spool having a second portion of larger diameter lthan the iirst portion and cooperating with a shoulder between the intermediate and largest diameter -bore portions to form an orice, the size of which varies in accordance with the axial lmovement of the spool in the loore, an inlet port in said valve body communicating with the bore portion of intermediate diameter, an exhaust port in said valve body communicating with the bore portion of largest diameter and a stylus movably mounted on said body and operably connected with said spool.

References Cited in the file of this patent UNITED STATES PATENTS 

